1. Field of the Invention
The present invention relates to a rotary variable resistor suitable for use in various types of electronic apparatuses.
2. Description of the Related Art
A conventional rotary variable resistor will be described with reference to FIGS. 7 and 8.
A substrate 31 made of a molded article of synthetic resin has a circular base 31a, a rectangular leader 31b, and a hole formed in the center of the base 31a.
Plural terminals 32 and 33 are made of metallic materials and are buried in the leader 31b of the substrate 31. Ends 32a and 33a of the terminals 32 and 33 project outward from a side of the leader 31b, and the other ends 32b and 33b are exposed at the surface of the substrate 31.
A first collector 34 made of a conductive material, such as silver, is formed on the surface of the substrate 31, and has an annular part 34a provided around the hole 31c, and a leader 34b leading from the annular part 34a to the leader 31b. The leader 34b is connected to the other end of one of the terminals 32.
A second collector 35 made of a conductive material, such as silver, is formed on the surface of the substrate 31, and has a circular-arc part 35a provided on the outer periphery of the annular part 34a and a leader 35b leading from the circular-arc part 35a to the leader 31b. The leader 35b is connected to the other end 32b of the other one of the terminals 32.
A first resistor 36 is formed on the surface of the substrate 31, and has a horseshoe-shaped resistance part 36a formed at the outer periphery of the circular-arc part 35a and a leader 36b linearly leading from both ends of the resistance part 36a to the leader 31b. The leader 36b is connected to the other end 33b of one of the terminals 33.
A second resistor 37 is formed on the surface of the substrate 31 and has a horseshoe-shaped resistance part 37a formed on the outer periphery of the resistance part 36a of the first resistor 36 and a leader 37b linearly leading from both ends of the resistance part 37a to the leader 31b. The leader 37b is connected to the other end 33b of one of the terminals 33.
The first and second resistance parts 36a and 37a are connected to each other at one end thereof.
A knob 38 made of an insulating material is shaped like a disk, and a hole 38 is formed in the center thereof. Two sliding elements 39 and 40 are fixed to the underside of the knob 38.
The sliding element 39 slides on the first collector 34 and the resistance part 36a of the first resistor 36, and the sliding element 40 slides on the second collector 35 and the resistance part 37a of the second resistor 37.
A shaft 37 is inserted through the hole 38a of the knob 38 and the hole 31c of the substrate 31 to thereby rotatably mount the knob 38 on the substrate 31.
When the knob 38 is rotated, the slider elements 39 and 40 are rotated, the slider element 39 slides on the first collector 34 and the first resistor 36 to vary the value of resistance between the terminals 32 and 33, and the slider element 40 slides on the second collector 35 and the second resistor 37 to vary the value of resistance between the terminals 32 and 33. This allows the two resistors 36 and 37 to be variable.
In the above-described conventional rotary variable resistor, since the first collector 34 has the leader 34b leading from the circular part 34a to the leader 31b of the substrate 31, a space for providing the leader 34b is required and the size of the resistor is thereby increased.
Therefore, the conventional rotary variable resistor is not suitable for size reduction.
In addition, the presence of the leader 34b interferes with the approach to both ends of the resistor 36. and therefore an effective angle of the resistor 36 is smaller.
Furthermore, in the first resistor 36, the leader 36b leading linearly from both ends of the resistance part 36a to the leader 31b is provided, and the leader 36b is connected to the other end 33b of one of the terminals 33. Therefore, the space of the leader 36b is increased, and is not suitable for size reduction.